1. Field of the Invention
The present invention relates to a plasma display apparatus and a driving method thereof.
2. Background of the Related Art
FIG. 1 shows a driving waveform of a conventional plasma display apparatus.
As shown in FIG. 1, a reset period can be divided into a set-up period and a set-down period.
In the set-up period, a ramp-up pulse is applied to a scan electrode Y, so that sufficient wall charges are accumulated on the scan electrode Y, a data electrode X and a sustain electrode Z.
In the set-down period, a ramp down pulse is applied to the sustain electrodes Z, so that the wall charges accumulated on the electrodes X, Y and Z are partially erased to ensure a uniform distribution of the wall charges on the electrodes X, Y and Z.
In an address period subsequent to a reset period, a scan pulse is applied to the scan electrode Y and a data pulse is applied to the data electrode X, so that a cell to be turned on is selected.
In a sustain period, sustain pulses having the same number as that of corresponding sub-fields to which the sustain pulses are allocated are applied to the selected cell in the address period, so that the selected cell is turned on.
Thereafter, in an erase period, as an erase pulse is applied to the Z electrode, wall charges that have been accumulated on the electrode are erased.
The reset period, the address period, the sustain period and the erase period are repeatedly performed in each of the sub-fields. In an address period of each sub-field, the width of the scan pulses applied to the scan electrode Y is constant as shown in FIG. 2.
A traverse axis of the graph shown in FIG. 2 indicates a scan pulse width and a longitudinal axis thereof indicates the location of the scan lines. That is, the width of scan pulses, which are applied to the scan lines from a first scan line at the top to a last scan line (Nth line) remains constant.
The number of scan lines increases as the size and resolution of a plasma display panel increases. Therefore, since the time allocated to one scan line for scanning becomes short, there is a difference between the amount of the wall charges on the first scan line and the amount of the wall charges on the last scan line (Nth line).
If the scan pulses having the same width are applied to the first scan line in the address period where wall charges are sufficiently accumulated by the set-up pulse applied in the reset period, the probability that an erroneous discharge or miswriting may occur decreases.
Since a significant amount of time elapses in the period from immediately after the reset period to when the last scan line (Nth line) is scanned, there is a high probability that wall charges, which are formed on the last scan line (Nth line) by the set-up pulse, may decrease. Therefore, if a width of a scan pulse applied to the first scan line is the same as the width of a scan pulse applied to the last scan line, an address discharge becomes unstable or the address margin decreases, and an exact driving of plasma display panel is difficult.
There is a difference in the amount of the wall charges on the respective scan lines depending on an Average Picture Level (APL) of each sub-field after a reset period. Therefore, if scan pulses having the same width are applied to the scan lines without considering an APL for each sub-field, there is a high probability of an erroneous discharge, miswriting, etc. may occur.